Concentrated and working strength aqueous flexographic developers

ABSTRACT

Flexographic printing members are prepared by developing an exposed flexographic printing member precursor with an aqueous flexographic developer. The aqueous flexographic developer comprises: a) a fatty acid composition consisting of one or more saturated or unsaturated fatty acids or alkali metal salts thereof, each saturated or unsaturated fatty acid or alkali metal salt thereof independently having 12 to 20 carbon atoms, the fatty acid composition being present in an amount of 0.25-2.0 weight %, and at least 85 weight % of the fatty acid composition is composed of one or more C18 mono- or poly-unsaturated fatty acids or alkali metal salts thereof; b) an aminopolycarboxylic acid or alkali metal salt thereof in an amount of 0.05-0.30 weight %; c) a buffer compound in an amount of 05-0.60 weight %; and d) water. Such aqueous flexographic developers can also be provided in concentrated form and appropriately diluted before or during use.

RELATED APPLICATIONS

Reference is made to the following commonly assigned and copendingpatent applications, the disclosures of which are incorporated herein byreference:

U.S. Ser. No. 15/352,666 filed on Nov. 16, 2016, by Ollmann, Fohrenkamm,Mellema, and Simpson), entitled “Methods of Forming FlexographicPrinting Members”

U.S. Ser. No. 15/196,122 filed Jun. 29, 2016; and

U.S. Ser. No. 15/196,132 filed Jun. 29, 2016.

FIELD OF THE INVENTION

This invention relates to working strength aqueous flexographicdevelopers and flexographic developer concentrates that can be used toprovide relief images in imagewise exposed flexographic printingprecursors. These developer compositions comprise one or more saturatedor unsaturated fatty acids or alkali metal salts thereof, at least oneunsaturated having Cis fatty acid (or alkali metal salt thereof) beingpredominant in concentration, an aminopolycarboxylic acid or saltthereof, and a buffering compound. Use of these compositions reduces theamount of residual debris on processed flexographic printing members.

BACKGROUND OF THE INVENTION

The production of relief images for flexographic printing is generallycarried out by imagewise exposing the photosensitive layer of aflexographic printing precursor using suitable imaging radiation such asUV radiation. Unexposed areas of the photosensitive layer are washed off(developed or “washed out”) using a suitable developer or processingsolution while exposed, and crosslinked areas are left intact. Residualdeveloper is generally removed by evaporation and if necessary, thedeveloped surface is treated to remove tackiness. A resultingflexographic printing plate having a relief image can be wrapped arounda cylinder on a printing press and used to transfer ink to a suitablesubstrate composed of various papers, polymeric films, fabrics,ceramics, and other materials. Alternatively, the resulting flexographicprinting member can be a flexographic printing sleeve that is slid ontoa suitable mandrel and used to similarly transfer ink to a substrate.

While the non-exposed photopolymer may be soluble in a variety oforganic solutions, only some of those organic-based developers do notdamage or swell the crosslinked portions while cleanly removing thenon-crosslinked portions. Swelling will eventually cause the reliefimage to deteriorate in the processing bath and the processing solutionwill have to be changed frequently due to the build-up of sludge. A widevariety of organic solvents and mixtures of solvents have been providedin the art and industry for this purpose.

However, for a variety of environmental and safety concerns, there hasbeen a strong incentive in the industry to avoid the use ofsolvent-based developers and to find aqueous-based flexographicdevelopers that will provide the same quality of processing as organicsolvent-based developers while avoiding environmental concernsassociated therewith. This has been difficult to achieve because of thenature of various photopolymer compositions designed for flexographicprinting precursors. Not just any type of aqueous solution, with orwithout water-miscible organic solvents will meet all of the rigorousprocessing and performance requirements.

For example, it is necessary that effective processing of an imagewiseexposed flexographic printing precursor remove all of the non-exposedphotopolymer, leaving relief images with well-defined boundaries (highresolution) and appropriate relief depth. Not just any developer,aqueous or non-aqueous, can be effective with a given photopolymercomposition.

Moreover, as an aqueous flexographic developer is used continuously toprocess numerous imagewise exposed precursors, the pH of the developercan change thereby causing more photopolymer components dispersedtherein to come out of solution and to re-deposit on the surface of therelief image. This reduces relief image resolution and results inserious image defects during printing. Such dispersed photopolymercomponents also can stick to brushes used during processing and cause“scum” on the relief image member. This problem increases as thedeveloper pH becomes more acidic.

U.S. Patent Application Publications 2007/0117039 (Wada et al) and2012/0288682 (Inoue et al.) describe aqueous developers used forsolubilizing non-exposed photopolymer compositions, which aqueousdevelopers include one or more nonionic or anionic surfactants and asuitable pH controlling agent.

U.S. Pat. No. 9,005,884 (Yawata et al.) proposes to solve such problemswith an aqueous flexographic developer that comprises both saturated andunsaturated fatty acids at a 20:80 to 80:20 weight ratio, along with analkali agent. Depending upon the particular ratio of saturated andunsaturated fatty acids, such compositions (also known as “soaps”) maynot sufficiently “develop” the exposed flexographic printing precursors,thereby leaving debris on the resulting flexographic printing plate,leading to severe printing defects in the resulting impressions.

In addition, it has been found that as the pH of such aqueous developersbecomes more acidic with continuous use, fatty acids incorporatedtherein are converted from their basic (ionic) form to their acidic formand their solubility in water and ability to form micelles are seriouslyreduced. When this happens, the debris from the non-exposed photopolymeris less solubilized in the absence of appropriate micelles. Bothprecipitated (solid) fatty acids and photopolymer debris floatthroughout the aqueous flexographic developer, collect on brushes usedduring processing, and end up as scum on the relief image of theprinting plate. These are unacceptable results in the industry and it toaddress these problems that the present invention is directed.

SUMMARY OF THE INVENTION

The present invention provides an aqueous flexographic developercomprising:

a) a fatty acid composition consisting of one or more saturated orunsaturated fatty acids or alkali metal salts thereof, each saturated orunsaturated fatty acid or alkali metal salt thereof independently having12 to 20 carbon atoms, the fatty acid composition being present in anamount of at least 0.25 weight % and up to and including 2 weight %;

wherein at least 85 weight % of the fatty acid composition is composedof one or more C₁₈ mono- or di-unsaturated fatty acids or alkali metalsalts thereof;

b) one or more aminopolycarboxylic acids or alkali metal salts thereofin an amount of at least 0.05 weight % and up to and including 0.30weight %;

c) a buffer compound in an amount of at least 0.05 weight % and up toand including 0.60 weight %; and

d) water in an amount of at least 97 weight % and up to and including99.5 weight %;

all amounts being based on the total weight of the aqueous flexographicdeveloper.

This invention also provides a flexographic developer concentratecomprising:

a) a fatty acid composition consisting of one or more saturated orunsaturated fatty acids or alkali metal salts thereof, each saturated orunsaturated fatty acid or alkali metal salt thereof independently having12 to 20 carbon atoms, the fatty acid composition being present in anamount of at least 10 weight % and up to and including 60 weight %,

wherein at least 85 weight % of the fatty acid composition is composedof one or more C₁₈ mono- or poly-unsaturated fatty acids or alkali metalsalts thereof;

b) one or more aminopolycarboxylic acids or alkali metal salts thereofin an amount of at least 1.5 weight % and up to and including 15 weight%; and

c) a buffer compound in an amount of at least 3.5 weight % and up to andincluding 25 weight %;

all amounts being based on the total weight of the flexographicdeveloper concentrate.

The present invention provides several advantages. It has been foundthat with the use of the working strength and concentrated flexographicdevelopers according to the present invention, the amount of debriscreated during developing (processing) exposed flexographic printingprecursors is reduced, and thus debris deposited (or “re-deposited”) onthe resulting flexographic printing members is reduced. This advantageis largely achieved because of the unique buffering in the compositionsand because of the presence of an aminopolycarboxylic acid chelatingagent such as EDTA or an alkali metal salt thereof (described below),thereby stabilizing the composition pH. With such a reduction in theformation and re-deposition of debris, improved images are reproduced onvarious substrates.

The working strength aqueous flexographic developers and concentratedforms thereof (solid or liquid) according to the present invention arecomposed of saturated and unsaturated fatty acids (or alkali metal saltsthereof) wherein mono- or poly-unsaturated fatty acids comprise at least85% of such fatty acids. The aqueous flexographic developers of thepresent invention are also unique in that they have reduced viscosity athigh concentrations and exhibit a viscosity maximum at certain lowerconcentrations.

While the present invention is not to be limited to or explained by aparticular mechanism, it is believed that the formation of a stableemulsion using a unique combination of fatty acids in the processingsolution is important to efficient flexographic processing (development)while minimizing the re-deposition of debris onto the processedflexographic printing members.

Another benefit of the present invention is that the working strengthaqueous flexographic developers and concentrated forms are moreenvironmentally friendly and less toxic or hazardous than manyflexographic developers used in the industry due to water being thepredominant solvent medium rather than organic solvents.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graphical representation of data for debris vs. processedflexographic printing plates obtained from some of the working examplesdescribed below.

DETAILED DESCRIPTION OF THE INVENTION

The following discussion is directed to various embodiments of thepresent invention and while some embodiments can be desirable forspecific uses, the disclosed embodiments should not be interpreted orotherwise considered to limit the scope of the present invention, asclaimed below. In addition, one skilled in the art will understand thatthe following disclosure has broader application than is explicitlydescribed in the discussion of any embodiment.

Definitions

As used herein to define various components of the working strengthaqueous flexographic developers, flexographic developer concentrates,and other materials used in the practice of this invention, unlessotherwise indicated, the singular forms “a,” “an,” and “the” areintended to include one or more of the components (that is, includingplurality referents).

Each term that is not explicitly defined in the present application isto be understood to have a meaning that is commonly accepted by thoseskilled in the art. If the construction of a term would render itmeaningless or essentially meaningless in its context, the term shouldbe interpreted to have a standard dictionary meaning.

The use of numerical values in the various ranges specified herein,unless otherwise expressly indicated otherwise, are considered to beapproximations as though the minimum and maximum values within thestated ranges were both preceded by the word “about.” In this manner,slight variations above and below the stated ranges may be useful toachieve substantially the same results as the values within the ranges.In addition, the disclosure of these ranges is intended as a continuousrange including every value between the minimum and maximum values aswell as the end points of the ranges.

The aqueous flexographic developers according to the present inventionare sometimes known as “washout” solutions or “processing solutions.”

The fatty acid compositions used in the present invention are sometimesknown in the art as “soaps” because they consist of one or more fattyacids or various chemical compositions and concentrations. Such fattyacid compositions can be in either liquid, gel, or solid form.

Unless otherwise indicated herein, the terms “concentrate,”“concentrated flexographic developer,” and “concentrated aqueousflexographic developer” are meant to refer to the same composition orsolution.

Unless otherwise indicated herein, the terms “photosensitive reliefimage precursor,” “flexographic printing member precursor,” and“precursor” are meant to refer to the same article.

Use of Invention

The compositions of the present invention are useful for preparingflexographic printing members after the appropriate “precursors” havebeen appropriately imaged.

In general, flexographic printing members can be formed after imaging aprecursor to provide latent images by applying a processing compositionaccording to the present invention. For example, some useful precursorsare described in U.S. Pat. No. 8,492,449 (Inoue et al.), the disclosureof which is incorporated herein by reference, as well as otherreferences cited below. Before this processing is carried out, thelatent image can be formed in the precursor using any appropriate methodknown in the art, for example using a mask image as described in U.S.Pat. No. 9,250,527 (Kidnie et al), the disclosure of which isincorporated herein by reference.

Flexographic Developers (Working Strength and Concentrates)

The flexographic developers according to the present invention can bemanufactured, provided for use, and potentially used either in anaqueous “working strength” form with diluted component concentrations,or as flexographic developer concentrates that can be either in solid orliquid form. Practically speaking, however, the concentrates aregenerally prepared in manufacturing and sold to users that typicallydissolve the concentrates in water or dilute the concentrates usingsuitable dilution rates to provide useful working strength compositionsfor a typical flexographic printing environment and equipment. While thecomponents making up both working strength and concentrated flexographicdevelopers are generally the same, their amounts, composition pH,composition viscosity, and other composition properties can be the sameor different.

In the following discussion, the various components that are common toboth working strength and concentrated flexographic developers will bedescribed, followed by specific discussions of the features relating tothe working strength aqueous flexographic developers and theflexographic developer concentrates according to the present invention.

Fatty Acid Composition:

An essential component of both the aqueous flexographic developers andthe flexographic developer concentrates is a “fatty acid composition”that consists of one or more saturated or unsaturated fatty acids (oralkali metal salts thereof). It is to be understood that within theaqueous flexographic developers described herein (and in the “fatty acidcomposition”), the fatty acids described below can be present inprotonated form or ionic form, or both protonated and ionic forms invarying amounts, depending upon pH.

Each of these saturated or unsaturated fatty acids (or alkali metalsalts thereof) independently have 12 to 20 carbon atoms. When multiplesaturated or unsaturated fatty acids (or alkali metal salts thereof) arepresent, they can have the same or different number of carbon atoms. Thealkali metal salts of the fatty acids can be sodium, potassium, orlithium salts, or a mixture of such salts. Typically, potassium saltsare desirable and can be obtained by mixing potassium ions (such as inthe form of potassium hydroxide) with the fatty acids.

It is essential for providing the advantages of the present inventionthat least 85 weight % and up to and including 100 weight % of the totalweight of the fatty acid composition consists of one or more mono- orpoly-unsaturated fatty acids (or alkali metal salts thereof). Inparticular, such unsaturated fatty acids are C₁₂ to C₂₀ mono- orpoly-unsaturated fatty acids (or alkali metal salts thereof). In manyembodiments, the one or more mono- or poly-unsaturated fatty acids (oralkali metal salts thereof) are present in an amount of at least 85weight % and up to and including 95 weight %, or even at least 85 weight% and up to and including 90 weight %, based on the total weight of thefatty acid composition. The poly-unsaturated fatty acids (or alkalimetal salts thereof) are generally di- and tri-unsaturated fatty acidsand the di-unsaturated fatty acids (or alkali metal salts thereof) areparticularly useful.

Representative useful saturated fatty acids (and alkali metal saltsthereof) having 12 to 20 carbon atoms include but are not limited to,lauric acid, sodium laurate, potassium laurate, myristic acid, sodiummyristate, potassium myristate, palmitic acid, sodium palmitate,potassium palmitate, stearic acid, sodium stearate, and potassiumstearate. Mixtures of two or more of these fatty acids (or alkali metalsalts thereof) can be used if desired. One or more potassium salts ofsuch saturated fatty acids are particularly useful.

Representative useful unsaturated fatty acids (including mono- andpolyunsaturated compounds) and alkali metal salts thereof having 12 to20 carbon atoms include but are not limited to, palmitoleic acid, sodiumpalmitoleate, potassium palmitoleate, oleic acid, sodium oleate,potassium oleate, linoleic acid, sodium linoleate, potassium linoleate,linolenic acid, sodium linolenate, potassium linolenate, ricinoleicacid, sodium ricinoleate, potassium ricinoleate, arachidonic acid,sodium arachidonate, and potassium arachidonate. The potassium salts ofsuch mono- and poly-unsaturated fatty acids are particularly useful. Insome embodiments, oleic acid, sodium oleate, or potassium oleate, or amixture thereof, is present as the unsaturated fatty acid, and suchunsaturated fatty acids (or alkali metal salts thereof) can comprise atleast 85 weight % and up to and including 100 weight % of the totalweight of the fatty acid composition. Mixtures of various mono- orpoly-unsaturated fatty acids (or alkali metal salts thereof) can also beused.

From the noted examples of useful fatty acids and alkali metal saltsthereof, any of the saturated or unsaturated fatty acids useful in thisinvention can be neutralized with an alkali metal agent such as sodiumhydroxide or potassium hydroxide.

As noted above, the fatty acid composition consists predominantly (atleast 85 weight %) of one or more mono- or poly-unsaturated fatty acids.Thus, the weight ratio of unsaturated fatty acids to saturated fattyacids (when present) can be from 5.67:1 to about 999:1.

Both saturated and unsaturated fatty acids (or alkali metal saltsthereof) useful in the present invention can be obtained from variouscommercial sources, or prepared using known starting materials andchemical syntheses that would be readily apparent to one skilled in theart.

Aminopolycarboxylic Acids:

A second essential component in the aqueous flexographic developers andflexographic developer concentrates is one or more aminopolycarboxylicacids or salts thereof (such as alkali metal salts). Such compoundscomprise one or more amino groups and two or more carboxylic acid groups(or salt groups) in the same molecule. Such compounds are sometimesknown in the art as chelating agents and have previously been used inthe photographic industry, when complexed with ferric ions, as bleachingagents.

Useful compounds of this type include but are not limited to,ethylenediamine tetraacetic acid (or salts thereof) known in the art asEDTA (or salt thereof), propylenediamine tetraacetic acid (or saltsthereof) known in the art as PDTA or other alkylenediamine tetraaceticacids (or salts thereof); diethylenetriamine pentaacetic acid (or saltsthereof); o-diamine cyclohexane tetraacetic acid (or salts thereof);ethylene glycol bis(aminoethyl ether) tetraacetic acid (or saltsthereof); diaminopropanol tetraacetic acid (or salts thereof);N-(2-hydroxyethyl)ethylenediamine triacetic acid (or salts thereof);nitrilotriacetic acid (or salts thereof) known in the art as NTA;iminodiacetic acid (or salts thereof) known in the art as ITA;ethyliminodipropionic acid (or salts thereof) known in the art as EIDPA,or other alkyliminodipropionic acids (or salts thereof);methyliminodiacetic acid (or salts thereof) known in the art as MIDA,ethyliminodiactic acid (or salts thereof) known in the art as EIDA, orother alkyliminodiacetic acids (or salts thereof); and other compoundsthat would be readily apparent to one skilled in the art from theserepresentative compounds. The sodium or potassium salts of EDTA areparticularly useful.

Mixtures of these various compounds can be used if desired.

Useful aminopolycarboxylic acids (or salts thereof) can be obtained fromvarious commercial sources or prepared using known starting materialsand chemical syntheses that would be readily apparent to one skilled inthe art.

Buffer Compounds:

A third essential component of the aqueous flexographic developers andflexographic developer concentrates is a buffer compound (or mixturethereof) that helps to maintain the desired pH during storage and use.Useful buffer compounds can be chosen by a skilled worker by consultingliterature describing known compounds having buffer capacity and the pHrange in which they are effective and matching such compounds to the pHconditions desired for the present invention. For example,representative buffer compounds useful in the present invention includebut are not limited to, a carbonate (such as potassium carbonate orsodium carbonate), sodium tetraborate, potassium tetraborate, sodiumphosphate, and potassium phosphate. Such materials are readily availablefrom various commercial sources.

Water:

Water is obviously essential to the aqueous flexographic developers andthe flexographic developer concentrates provided in liquid formaccording to this invention and is the predominant solvent used therein.This means that organic solvents (both water-miscible andwater-immiscible organic solvents) are generally present only in minoramounts or particularly in an amount of less than 10 weight % of thetotal aqueous flexographic developer or flexographic developerconcentrate weight, and in most embodiments, such organic solvents arepresent in an amount of 0 weight % and up to and including 5 weight %,based on the total flexographic developer weight (whether in liquid orsolid form). Any suitable quality of water can be used, but generally,the water is deionized water or water obtained using distillation orreverse osmosis.

Optional Addenda:

Materials that are optional but that can be included in the aqueousflexographic developers or flexographic developer concentrates forcertain purposes include glycol and poly-glycol mono-ether co-solvents,enzymes, fluorescent whitening agents, perfumes, biocide, fungicides,defoaming agents, colorants, bleach, bleach activators, and surfactants.

For example, one or more glycol and poly-glycol mono-ether co-solventscan be present in each type of composition, which compounds generallyhave a molecular weight of less than 150, are water-soluble, and have atleast one hydroxy group. One useful compound of this type is propyleneglycol butyl ether that can be obtained as DOWANOL® PnB from DowChemical Company. Such glycol and poly-glycol mono-ether co-solvents canbe present in an amount of at least 0.05 weight % and up to andincluding 0.30 weight %, based on the total weight of the aqueousflexographic developer. The amount of the glycol and poly-glycolmono-ether co-solvents in the flexographic developer concentrates (solidor liquid form) can be readily determined based on the dissolution rateor dilution rate of a liquid concentrate to provide the desired workingstrength aqueous flexographic developers. Typically, the amount of theone or more glycol and poly-glycol mono-ether-co-solvents in theconcentrates is at least 1.5 weight % and up to and including 15 weight%, based on the total weight of flexographic developer concentrate.Other useful glycols and poly-glycol mono-ethers include but are notlimited to, 2-phenoxyethanol, 1-ethoxy-2-propanol, 2-methoxypropanol,diethyleneglycol monobutyl ether, 2-butoxyethanol, and propylene glycolpropyl ether.

Working Strength Aqueous Flexographic Developers:

In general, at working strength, each aqueous flexographic has a pH ofat least 9.5 and up to and including 11.5, more likely of at least 9.8and up to and including 11.2, or most likely of at least 10.1 and up toand including 10.5. It is desirable to keep the pH of such workingstrength aqueous flexographic developers during use within ±0.5 of theoriginal pH (pH when processing is begun). The aqueous flexographicdevelopers according to the present invention generally exhibit improvedpH stability upon storage and use.

Since the amounts of the various components (described below) in theworking strength aqueous flexographic developers are quite low, theviscosity of the working strength composition does not significantlyvary from that of water.

The fatty acid composition described above is generally present in theworking strength aqueous flexographic developers in an amount of atleast 0.25 weight % and up to and including 2.0 weight %, or of at least0.5 weight % and equal to or less than 1.25 weight %, based on the totalweight of the aqueous flexographic developer.

The one or more aminopolycarboxylic acids (or salts thereof) describedabove can be present in the working strength aqueous flexographicdeveloper in an amount of at least 0.05 weight % and up to and including0.30 weight %, or more likely of at least 0.05 and up to and including0.25 weight %, based on the total weight of the aqueous flexographicdeveloper.

One or more buffer compounds are generally present in the workingstrength aqueous flexographic developers in suitable amounts to maintainthe desired pH. For example, they can be present in an amount of atleast 0.05 weight % and up to and including 0.60 weight %, or at least0.20 weight % and up to and including 0.60 weight %, based on the totalweight of the aqueous flexographic developer.

Water is generally present in the working strength aqueous flexographicdevelopers in an amount of at least 97 weight % and up to and including99.5 weight %, or even at least 97.5 weight % and up to and including99.0 weight %, based on the total weight of the aqueous flexographicdeveloper.

Flexographic Developer Concentrates:

Each flexographic developer concentrate (in liquid form) can have a pHthat is the same as or different from that working strength aqueousflexographic developer that is formed upon dilution. In general, eachconcentrate can have a pH of at least 9.5 and up to and including 11.5,more likely of at least 9.8 and up to and including 11.2, or most likelyof at least 10.3 and up to and including 10.9.

The viscosity of each concentrate can be at least 100 centipoises (0.1Pascal sec) and up to and including 900 centipoises (0.9 Pascal sec), ormore likely at least 300 centipoises (0.3 Pascal sec) and up to andincluding 600 centipoises (0.6 Pascal sec), all measured using astandard viscometer at 25° C.

The fatty acid composition described above is generally present in theconcentrate in an amount of at least 10 weight % and up to and including60 weight %, or even at least 12 weight % and equal to or less than 25weight %, based on the total weight of the concentrate.

The one or more aminopolycarboxylic acids (or salts thereof) describedabove can be present in the concentrate in an amount of at least 1.5weight % and up to and including 15 weight %, or more likely of at least1.5 and up to and including 10 weight %, based on the total weight ofthe flexographic developer concentrate.

One or more buffer compounds are generally present in the flexographicdeveloper concentrate in suitable amounts to maintain the desired pH.For example, they can be present in an amount of at least 3.5 weight %and up to and including 25 weight %, or at least 4 weight % and up toand including 8 weight %, based on the total weight of the flexographicdeveloper concentrate.

The amount of water in the flexographic developer concentrates, if inliquid form, is determined by considering the dilution ratio needed toprovide a suitable working strength aqueous flexographic developer asdescribed above, or to provide a suitable replenisher concentration (asdescribed below). In general, the amount of water in the concentratescan be up to and including 85 weight %, or at least 60 weight % and upto and including 80 weight %, based on the total weight of theflexographic developer concentrates in liquid form.

The aqueous flexographic developers according to the present inventioncan be prepared by any method wherein the three essential componentsdescribed above and any optional addenda are added to water in anydesirable order and the resulting solution or composition is thenstirred to provide homogenization. The mixing method can be carried outat any suitable temperature that does not deteriorate the composition orits utility to process exposed flexographic printing member precursors.The essential components and optional addenda can be incorporated inwater in suitable amounts to form either a concentrate (in liquid form)or a working strength composition of any desired concentration andviscosity.

Solid form flexographic developer concentrates can be prepared byallowing a fatty acid (or mixture thereof) and an alkali metal base toreact in water, evaporating the water, adding the remaining desiredcomponents, and pulverizing the resulting dry composition. Thus, wateris absent and the solid concentrate can then be dissolved in a suitableamount of water and mixed to provide any of i) a desired aqueousflexographic developer, ii) a liquid form flexographic developerconcentrate; iii) a replenisher developer composition, or iv) areplenisher developer concentrate.

Forming Flexographic Printing Members

To provide a flexographic printing member such a flexographic printingplate or flexographic printing sleeve, containing a relief image, asuitable flexographic printing precursor is imagewise exposed (asdescribed below) followed by suitable processing using an aqueousflexographic developer according to the present invention.

Useful flexographic printing member precursors are described in moredetail below in reference to the formation of flexographic printingplates but it is to be understood that the flexographic printing sleevescan be similarly prepared.

Some useful photosensitive relief image precursors or flexographicprinting member precursors are described in U.S. Pat. No. 8,142,987 (Aliet al.), U.S. Pat. No. 7,226,709 (Kidnie et al.), U.S. Pat. No.7,348,123 (Mengel et al.), U.S. Pat. No. 8,945,813 (Kidnie), and U.S.Pat. No. 9,005,884 (noted above), and U.S. Patent ApplicationPublications 2007/0117039 (Wada et al.) and 2012/0288682 (Inoue et al),the disclosures of all of which are incorporated herein by reference.

Such useful precursors are generally composed of a photosensitive orphotopolymerizable elastomer or photosensitive elastomeric imageablelayer composition disposed on a suitable support or substrate. By“photosensitive” or “photopolymerizable,” is meant that the elastomericimageable layer composition is polymerizable or crosslinkable fromirradiation by suitable radiation, or both polymerizable andcrosslinkable. The photosensitive elastomeric imageable layercomposition generally includes a thermoplastic binder, at least onemonomer and an initiator (photoinitiator) that is sensitive to suitableradiation such as visible or UV radiation, or both. Various polymericbinders are known in the art as described in the publications noted inthe preceding paragraph. Poly(styrene/isoprene/styrene) andpoly(styrene/butadiene/styrene) block copolymers are useful, as well asvarious synthetic or natural polymers of conjugated hydrocarbons,including polyisoprene, 1,2-polybutadiene, and butadiene/acrylonitrile.

The “monomer” is generally considered a compound that is compatible withthe polymeric binder and is capable of addition polymerization inresponse to irradiation with actinic radiation. There can be a mixtureof monomers if desired. They typically have a molecular weight less than5000 although compounds with higher molecular weight can be used ifdesired. Useful monomers include but are not limited to, variousacrylates, methacrylates, mono- and polyesters of alcohols and polyolssuch as polyacrylates and polymethacrylates. Photoinitiators can includebut are not limited to, compounds that generate free radicals uponexposure to actinic radiation such as quinones, benzophenones, benzoinethers, aryl ketones, peroxides, biimidazoles, benzyl dimethyl ketal,and others known in the art.

The photosensitive elastomeric imageable layer composition can alsoinclude various additives such as colorants, processing aids,antioxidants, and antiozone agents as are known in the art.

Additionally, a protective cover sheet can be placed over thephotosensitive elastomeric imageable layer composition, which coversheet contains a protective polymer. Generally, the protective layer istransparent and has little tackiness before irradiation. It can bewashed away or removed using the aqueous flexographic developersdescribed above according to the present invention. Examples of polymerssuitable for preparing this cover sheet include but are not limited to,polyamides and cellulose esters such as cellulose acetate butyrate andcellulose acetate propionate (for example, see U.S. Pat. No. 6,030,749of Takahashi et al., Cols. 4-8 of U.S. Pat. No. 9,005,884, noted above,Cols. 7-8), the disclosures of both of which are incorporated herein byreference.

Useful precursors can also contain suitable infrared radiation-sensitivelayers as described in the publications incorporated above.

Flexographic printing member precursors useful in the present inventioncan be imaged by exposure to suitable imaging (also known as “curing”)radiation through a suitable mask image to form an imaged flexographicprinting member precursor. The curing radiation is blocked by the maskimage in non-exposed regions and the exposed regions are hardened orcured. Exposure can be accomplished by floodwise exposure from suitableirradiation sources (visible light or UV radiation), for example havinga wavelength of at least 150 nm and up to and including 750 nm, or at awavelength of from at least 300 and up to and including 450 nm from asuitable irradiation source or UV radiation. The time for exposure willdepend upon the nature and thickness of the flexographic printing memberprecursor and the source of the radiation. For example, usefulcommercial flexographic printing member precursors such as EastmanKodak's FLEXCEL brand precursors and. DuPont's Cyrel® brand precursorscan be imaged on commercial apparatus known in the art. If desired, bothfrontside and backside exposures can be carried out, or exposure can becarried out on only a single side of the precursor.

An aqueous flexographic developer according to the present invention canbe applied to an exposed flexographic printing member precursor in anysuitable manner including but not limited to spraying, brushing,rolling, dipping (immersing), or any combination thereof. This removesuncured or non-polymerized regions of the photosensitive elastomericimageable layer composition.

This processing is typically carried out using a working strengthaqueous flexographic developer according to the present invention thatis provided as manufactured, but more likely is provided by dissolvingor dilution of a flexographic developer concentrate according to thepresent invention. An acceptable dilution rate of a concentrate inliquid form is mixing 1 part of the concentrate with at least 2 partsand up to and including 99.8 parts of water, or more likely at least 20parts and up to and including 99 parts of water.

Development or processing is usually carried out under conventionalconditions such as for at least 5 minutes and up to and including 20minutes and at a temperature of at least 23° C. and up to and including32° C. The specific development conditions will be dictated by the typeof apparatus used and the specific concentration of components in theaqueous flexographic developer.

During processing, evaporation and resulting flexographic printingmembers can carry away some of the water in the working strength aqueousflexographic developer. As a result, the development strength (activity)of usefulness of various components can be diminished. It can be usefulthen to “replenish” the working strength aqueous flexographic developerwith a replenisher developer composition that has the same or a greaterconcentration of the one or more of the essential components a) throughc) and any optional components as the original working strength aqueousflexographic developer, A skilled worker would be able to formulate asuitable replenisher developer composition for a given apparatus andprocessing through put.

When a flexographic developer concentrate, in liquid form, is suppliedto the processing apparatus and appropriately diluted as described aboveto form an aqueous flexographic developer, a replenisher developercomposition can be supplied to the processing apparatus using knownprocedures and apparatus features. Alternatively, or in addition to thisdescribed replenishment procedure, the flexographic developerconcentrate (in liquid form) also can be replenished before the dilutionprocess using a replenisher developer concentrate that can have the sameor different concentration of components a) through c) and any optionalcomponents, as the “original” flexographic developer concentrate.

Particularly useful processing methods and systems useful in carryingout the present invention are described in U.S. Ser. Nos. 15/196,122 and15/196,132 (both noted above).

Post-developing processing of the relief image in the flexographicprinting member may be desirable under some circumstances. Typicalpost-development processing includes drying the relief image to removeany excess processing solution and post-curing by exposing the reliefimage to curing radiation to cause further hardening or crosslinking.The conditions for these processes are well known to those skilled inthe art. For example, the relief image may be blotted or wiped dry ordried in a forced air or infrared oven. Drying times and temperatureswould be readily apparent to one skilled in the art.

Detackification can be carried out if the flexographic printing memberis still tacky after drying. Such treatments, for example, by treatmentwith bromide or chlorine solutions or exposure to UV or visibleradiation, are well known to a skilled artisan.

The resulting relief image may have a depth of from about 2% to about100% (typically from about 10 to about 80%) of the original thickness ofthe photosensitive elastomeric imageable layer composition in theflexographic printing member precursor. For example, if thephotosensitive elastomeric imageable layer composition is disposed on anon-photosensitive support, up to 100% of it can be removed in part orall of the relief image. The relief image depth can be from about 150 toabout 2000 μm.

The flexographic printing members can be used to advantage in theformation of seamless, continuous flexographic printing webs, or theycan be formed as flat sheets that can be wrapped around a cylinder form,for example as a flexographic printing plate or a flexographic printingsleeve. Alternatively, the photosensitive elastomeric imageable layercomposition can be mounted around a cylindrical form for imaging anddevelopment.

The present invention provides at least the following embodiments andcombinations thereof, but other combinations of features are consideredto be within the present invention as a skilled artisan would appreciatefrom the teaching of this disclosure:

1. An aqueous flexographic developer comprising:

a) a fatty acid composition consisting of one or more saturated orunsaturated fatty acids or alkali metal salts thereof, each saturated orunsaturated fatty acid or alkali metal salt thereof independently having12 to 20 carbon atoms, the fatty acid composition being present in anamount of at least 0.25 weight % and up to and including 2.0 weight %;

wherein at least 85 weight % of the fatty acid composition is composedof one or more C₁₈ mono- or poly-unsaturated fatty acids or alkali metalsalts thereof;

b) one or more aminopolycarboxylic acids or alkali metal salts thereofin an amount of at least 0.05 weight % and up to and including 0.30weight %;

c) a buffer compound in an amount of at least 0.05 weight % and up toand including 0.60 weight %; and

d) water in an amount of at least 97 weight % and up to and including99.5 weight %;

all amounts being based on the total weight of the aqueous flexographicdeveloper.

2. The aqueous flexographic developer of embodiment 1, wherein the fattyacid composition is present in an amount equal to or less than 1.25weight % based on the total weight of the aqueous flexographicdeveloper.

3. The aqueous flexographic developer of embodiment 1 or 2, comprisingethylenediamine tetracarboxylic acid or an alkali metal salt thereof inan amount of at least 0.05 weight % and up to and including 0.30 weight%, based on the total weight of the aqueous flexographic developer.

4. The aqueous flexographic developer of any of embodiments 1 to 3,further comprising at least 0.05 weight % and up to and including 0.30weight % of a glycol and poly-glycol mono-ether co-solvent having amolecular weight of less than 150, the amount being based on the totalweight of the aqueous flexographic developer.

5. The aqueous flexographic developer of embodiment 4, wherein:

a) the fatty acid composition consists essentially of oleic acid or analkali metal salt thereof in an amount of at least 90 weight % and up toand including 100 weight % of the fatty acid composition, and the fattyacid composition is present in an amount of at least 0.50 weight % andup to and including 1.25 weight %;

b) ethylenediamine tetracarboxylic acid or an alkali metal salt thereofis present as the one or more aminopolycarboxylic acids or alkali metalsalts thereof in an amount of at least 0.05 weight % and up to andincluding 0.25 weight %; and

c) a carbonate is present as the buffer compound in an amount of atleast 0.20 weight % and up to and including 0.60 weight %;

all amounts being based on the total weight of the aqueous flexographicdeveloper.

6. A flexographic developer concentrate comprising:

a) a fatty acid composition consisting of one or more saturated orunsaturated fatty acids or alkali metal salts thereof, each saturated orunsaturated fatty acid or alkali metal salt thereof independently having12 to 20 carbon atoms, the fatty acid composition being present in anamount of at least 10 weight % and up to and including 60 weight %,

wherein at least 85 weight % of the fatty acid composition is composedof one or more Cis mono- or poly-unsaturated fatty acids or alkali metalsalts thereof;

b) one or more aminopolycarboxylic acids or alkali metal salts thereofin an amount of at least 1.5 weight % and up to and including 15 weight%; and

c) a buffer compound in an amount of at least 3.5 weight % and up to andincluding 25 weight %;

all amounts being based on the total weight of the flexographicdeveloper concentrate.

7. The flexographic developer concentrate of embodiment 6, furthercomprising:

d) water in an amount of up to and including 85 weight %, based on thetotal weight of the flexographic developer concentrate.

8. The flexographic developer concentrate of embodiment 6 or 7, whereinthe fatty acid composition is present in an amount equal to or less than25 weight %, based on the total weight of the flexographic developerconcentrate.

9. The flexographic developer concentrate of any of embodiments 6 to 8,comprising ethylenediamine tetracarboxylic acid or an alkali metal saltthereof in an amount of at least 1.5 weight % and up to and including 10weight %, based on the total weight of the flexographic developerconcentrate.

10. The flexographic developer concentrate of any of embodiments 6 to 9,further comprising at least 1.5 weight % and up to and including 15weight % of a glycol and poly-glycol mono-ether co-solvent having amolecular weight of less than 150, the amount being based on the totalweight of the flexographic developer concentrate.

11. The flexographic developer concentrate of any of embodiments 6 to10, having a viscosity of at least 100 centipoises and up to andincluding 900 centipoises.

12. The flexographic developer concentrate of any of embodiments 6 to11, having a viscosity of at least 300 centipoises and up to andincluding 600 centipoises.

13. The flexographic developer concentrate of any of embodiments 6 and 8to 12 that is in solid form.

14. The flexographic developer concentrate of any of embodiments 6 to 13that is in liquid form and comprises up to 85 weight %, based on thetotal weight of the aqueous flexographic developer concentrate.

15. Any of embodiments 1 to 12 and 14 that has a pH of at least 9.5 andup to and including 11.5.

16. Any of embodiments 1 to 12, 14, and 15 that has a pH of at least 9.8and up to and including 11.2.

17. Any of embodiments 1 to 16, wherein the fatty acid compositionconsists essentially of oleic acid or an alkali metal salt thereof in anamount of at least 85 weight % and up to and including 90 weight %,based on the total weight of the fatty acid composition.

18. Any of embodiments 1 to 17, wherein the buffer compound is acarbonate.

The following Examples are provided to illustrate the practice of thisinvention and are not meant to be limiting in any manner. Unlessotherwise indicated, the materials used in the working examples wereobtained from various commercial sources.

COMPARATIVE EXAMPLE 1

A flexographic developer concentrate was prepared outside of the presentinvention by allowing a fatty acid mixture to react with potassiumhydroxide. Glycerin was added and the pH was adjusted to 9.8. Water wasadded to bring the solids concentration to 21 weight %. The finalflexographic developer concentrate had the following components andamounts (weight %):

Lauric acid 4.03% Myristic acid 1.47% Palmitic acid 1.31% Steric acid0.88% Oleic acid 8.28% Linoleic acid 0.58% Potassium hydroxide 3.72%Glycerin 0.73% Water 79.00%

This flexographic developer concentrate was made into an aqueousflexographic developer (working strength solution) by diluting 1 part ofthe noted flexographic developer concentrate with 42 parts of water toprovide an aqueous flexographic developer having a total amount ofsaturated and unsaturated fatty acid, fatty acid salts, and glycerin of0.5 weight %, and a pH of 9.5. The resulting aqueous flexographicdeveloper was placed in an orbital processor unit and used to processexposed flexographic printing plates like those described in U.S. Pat.No. 8,492,449 (noted above), except such precursors contained noanti-adhesive layer over the photopolymer layer, using known conditionsand procedures for such flexographic printing member precursors. Theamount of debris on the processed flexographic printing plates wasevaluated and assigned a numerical value between 1 and 5 with 1 meaningno debris and 5 meaning an unacceptable amount of debris.

INVENTION EXAMPLE 1

A flexographic developer concentrate was prepared according to thepresent invention by allowing a fatty acid mixture to react withpotassium hydroxide. The pH was adjusted to 10.6 and water was added tobring the solids concentration to 21 weight %. The final flexographicdeveloper concentrate had the following components and amounts:

Palmitic acid 0.04% Steric acid 0.46% Oleic acid 15.77% Linoleic acid1.24% Linolenic acid 0.02% Potassium hydroxide 3.48% Water 79.00%

One part of this concentrate was diluted with 42 parts of water toprovide an aqueous flexographic developer having a total fatty acid andfatty acid salt concentration of 0.5 weight % and a pH of 10.5. Theresulting aqueous flexographic developer was placed in an orbitalprocessor unit and used to process exposed flexographic printing platesas described above in Comparative Example 1, using known conditions andprocedures for such flexographic printing member precursors. The amountof debris on the processed flexographic printing plates was evaluatedand assigned a numerical value as described for Comparative Example 1.

INVENTION EXAMPLE 2

A flexographic developer concentrate was prepared according to thepresent invention by allowing a fatty acid mixture to react withpotassium hydroxide. Potassium carbonate was added and the pH wasadjusted to 10.6. Water was added to bring the solids concentration to21 weight %. The final flexographic developer concentrate had thefollowing components and amounts:

Palmitic acid 0.03% Steric acid 0.33% Oleic acid 11.19% Linoleic acid0.88% Linolenic acid 0.01% Potassium hydroxide 2.47% Potassium carbonate6.09% Water 79.00%

One part of the resulting flexographic developer concentrate was dilutedwith 42 parts of water to provide an aqueous flexographic developerhaving a total fatty acid and fatty acid salt amount of 0.5 weight % anda pH of 10.5.

This aqueous flexographic developer was placed in an orbital processorunit and used to process exposed flexographic printing plates asdescribed above in COMPARATIVE EXAMPLE 1, using known conditions andprocedures for such flexographic printing member precursors. The amountof debris on the processed flexographic printing plates was evaluatedand assigned a numerical value as described for COMPARATIVE EXAMPLE 1.

INVENTION EXAMPLE 3

A flexographic developer concentrate was prepared according to thepresent invention by allowing a fatty acid mixture to react withpotassium hydroxide. Potassium carbonate and EDTA disodium salt wereadded and the pH was adjusted to 10.6. Water was added to bring thesolids concentration to 21 weight %. The final flexographic developerconcentrate had the following components and amounts:

Palmitic acid 0.02% Steric acid 0.29% Oleic acid 10.00% Linoleic acid0.79% Linolenic acid 0.01% Potassium hydroxide 2.21% Potassium carbonate5.44% EDTA disodium salt 2.25% Water 79.00%

One part of the resulting flexographic developer concentrate was dilutedwith 42 parts of water to provide an aqueous flexographic developerhaving a total fatty acids and fatty acid salts content of 0.5 weight %and a pH of 10.5.

The aqueous flexographic developer was placed in an orbital processorunit and used to process exposed flexographic printing plates asdescribed above in COMPARATIVE EXAMPLE 1, using known conditions andprocedures for such flexographic printing member precursors. The amountof debris on the processed flexographic printing plates was evaluatedand assigned a numerical value as described for COMPARATIVE EXAMPLE 1.

INVENTION EXAMPLE 4

A flexographic developer concentrate was prepared according to thepresent invention by allowing a fatty acid mixture to react withpotassium hydroxide. Potassium carbonate, EDTA disodium salt, andDOWANOL® PnB co-solvent were added. The pH was adjusted to 10.6 andwater was added to bring the solids concentration to 21 weight %. Thefinal flexographic developer concentrate had the following make up:

Palmitic acid 0.02% Steric acid 0.26% Oleic acid 9.03% Linoleic acid0.71% Linolenic acid 0.01% Potassium hydroxide 1.99% DOWANOL ® PnB 2.03%Potassium carbonate 4.91% EDTA disodium salt 2.03% Water 79.00%

One part of the resulting flexographic developer concentrate was dilutedwith 199 parts of water to provide an aqueous flexographic developerhaving a total fatty acid salts content of 0.5 weight % and a pH of10.5.

The resulting aqueous flexographic developer was placed in an orbitalprocessor unit and used to process exposed flexographic printing platesas described above in COMPARATIVE EXAMPLE 1, using known conditions andprocedures for such flexographic printing member precursors. The amountof debris on the processed flexographic printing plates was evaluatedand assigned a numerical value as described for COMPARATIVE EXAMPLE 1.

Evaluation of Debris Levels on Processed Flexographic Printings:

The flexographic printing plate precursors described above were exposedin a standard fashion using a FLEXEL mask and lamination system with thesame standard back exposures and main exposures. The exposed precursorswere processed using an orbital brush processor that is commonly used inthe industry. The debris level for each processed flexographic printingplate was evaluated under a light microscope. A higher level of debriswas given a higher score as described above, and the higher the amountof debris, the worse the printing results.

The following results were determined for the Examples described above:

Average Debris Score Example Plates 1-5 5-10 10-15 Comparative 1 1.6 1.72.2 Invention 1 1.2 1.5 1.8 Invention 2 0.9 0.9 1.0 Invention 3 0.75 1.01.0 Invention 4 0.80 0.95 1.0

Comparison of the Debris Levels on Printing Plates Prepared UsingComparative Example 1 and Invention Example 4:

A number of imagewise exposed flexographic printing plate precursorswere processed in the processing unit as described above. As the numberof flexographic printing plate precursors being processed increased, theamount of debris from the non-exposed material in the aqueousflexographic developer increased, leading to increased debris on thefinished flexographic printing plates. FIG. 1 shows the debris levelobserved vs. the number of flexographic printing plates that wereprocessed using the aqueous flexographic developers of both COMPARATIVEEXAMPLE 1 and Invention Example 4. The observed debris was found on theresulting flexographic printing plates. The solid line data representthe results obtained using COMPARATIVE EXAMPLE 1 and the dashed linedata represent the results obtained using Invention Example 4. Bothillustrated lines represent an average of the respective data pointswherein each datum point represents an individual processed flexographicprinting plate.

It is evident that while observed debris increased as the number ofprocessed flexographic printing plates was increased in bothcompositions (that is, as the aqueous developer composition was“seasoned” from use), the Invention Example 4 aqueous flexographicdeveloper provided a reduction in debris formation as the number ofprocessed flexographic printing plates increased, compared to theaqueous developer composition of COMPARATIVE EXAMPLE 1.

INVENTION EXAMPLE 5

A flexographic developer concentrate was prepared according to thepresent invention containing the following components and had a pH of10.6. No saturated fatty acids (or alkali metal salts thereof) wereincluded and the fatty acid composition contained only potassium oleate.

Potassium oleate at 54.9 weight %;

Potassium carbonate at 23.1 weight %;

EDTA di sodium salt at 10.0 weight %; and

Propylene glycol n-butyl ether at 11.0 weight %.

COMPARATIVE EXAMPLE 2

A flexographic developer concentrate was prepared outside of the presentinvention but according to the teaching in U.S. Pat. No. 9,005,884(noted above) in which the weight ratio of unsaturated fatty acids (oralkali metal salts thereof) to saturated fatty acids (or alkali metalsalts thereof) was 80:20. The concentrate components were as follows andthe concentrate had a pH of 10.6:

Potassium oleate (mono-unsaturated) at 79.4 weight %;

Potassium Stearate (saturated) at 20.1 weight %; and

Potassium Hydroxide at 0.5 weight %.

COMPARATIVE EXAMPLE 3

Another flexographic developer concentrate was prepared outside of thepresent invention but according to the teaching in U.S. Pat. No.9,005,884 (noted above) in which the weight ratio of unsaturated fattyacids (or alkali metal salts thereof) to saturated fatty acids (oralkali metal salts thereof) was 20:80. The concentrate had a pH of 10.7and its components were as follows:

Potassium Oleate at 20.1 weight %;

Potassium Stearate at 79.4 weight %; and

Potassium Hydroxide at 0.5 weight %.

Each of the concentrates of Invention Example 5 and Comparative Examples2 and 3 were used to make working strength aqueous flexographicdevelopers by diluting one part of each with 116.6 parts of water toprovide 0.85 weight % solids. The resulting working strength aqueousflexographic developers had a pH of 10.4, 10.5, and 10.5, respectively.

Samples of flexographic printing plates as described in COMPARATIVEEXAMPLE 1 were back exposed at each of 30 seconds, 45 seconds, 60seconds, and 75 seconds using a Mekrom Concept 302 EDLF exposure unit toestablish a “plate floor” (Plate 1). A section of each printing platesample that had been exposed at 75 seconds was given a front exposure(“main exposure”) of 8 minutes to provide a fully exposed printing“plate ceiling”.

Each exposed flexographic printing plate precursor was then processed(developed) with each of the working strength aqueous flexographicdevelopers of Invention Example 5 and Comparative Examples 2 and 3 in aTakano A-Flexo A2W Plate Processor for 4 minutes at 54° C. Bysubtracting the thickness of the plate floor from the thickness of theplate ceiling, a flexographic printing plate relief value was obtainedfor the various back exposures and a back exposure value for a desiredrelief value was determined.

Using the values determined above for the aqueous flexographicdevelopers of Invention Example 5 and Comparative Examples 2 and 3,flexographic printing plates (precursors) like those described inComparative Example 1 were back exposed. These flexographic printingplate were then exposed imagewise with a main exposure of various times(Plate 2) and processed as described above using the aqueousflexographic developers of Invention Example 5 and Comparative Examples2 and 3, respectively. By examining the quality of the features from themain exposure values, an optimal main exposure was determined for eachaqueous flexographic developer.

Six additional samples of the noted flexographic printing plates(precursors) (3^(nd) through 8^(th) plates) were processed withoutexposure using each of the three aqueous flexographic developers toincrease the amount of solid material in each processing bath.

Two more samples of the flexographic printing plate described above inCOMPARATIVE EXAMPLE 1 (“9^(th) and 10^(th) plates”) were each exposedusing a test pattern and a main exposure value that encompassed thedetermined optimum values (as determined using plates 1 and 2 describedabove, as shown below in TABLE I). The level of debris on each of the9^(th) and 10^(th) plates was examined and assigned a relative valuefrom 1.0 to 6.0 with 1.0 being good. The initial pH of each aqueousflexographic developer was measured, the respective decreased pH valueswere measured after processing of the 10^(th) plate, and the absolute pHdifference was determined. The results of this experimentation are shownin the following TABLE I.

TABLE I Main Back Exposure Debris Debris Exposure Value 9^(th) MainLevel Level Developer Value plate Expo- 9^(th) 10^(th) pH Example(seconds) (minutes) sure plate plate Change Invention 57 12 14 0.8 1.00.35 5 Compar- 65 11 12 4.9 5.4 0.75 ative 2 Compar- 69 11 12 4.6 5.11.6 ative 3

The results shown in TABLE I indicate that the debris level for plates 9and 10 and the pH change of the aqueous flexographic developer ofInvention Example 5 are much lower than for the aqueous flexographicdevelopers of Comparative Examples 2 and 3.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

The invention claimed is:
 1. A flexographic developer concentrate forprocessing an imaged flexographic printing member precursor, comprising:a) a fatty acid composition consisting of one or more saturated orunsaturated fatty acids or alkali metal salts thereof, each saturated orunsaturated fatty acid or alkali metal salt thereof independently having12 to 20 carbon atoms, the fatty acid composition being present in anamount of at least 10 weight % and up to and including 60 weight %,wherein at least 85 weight % of the fatty acid composition is composedof one or more C₁₈ mono- or poly-unsaturated fatty acids or alkali metalsalts thereof; b) one or more aminopolycarboxylic acids or alkali metalsalts thereof in an amount of at least 1.5 weight % and up to andincluding 15 weight %; c) a buffer compound in an amount of at least 3.5weight % and up to and including 25 weight %; and d) water in an amountof up to and including 85 weight %, based on the total weight of theflexographic developer concentrate, all amounts being based on the totalweight of the flexographic developer concentrate, the flexographicdeveloper concentrate having a pH of at least 9.8 and up to andincluding 11.2 and a viscosity of at least 100 centipoises and up to andincluding 900 centipoises, and further comprising at least 1.5 weight %and up to and including 15 weight % of a glycol and poly-glycolmono-ether co-solvent having a molecular weight of less than 150, theamount being based on the total weight of the flexographic developerconcentrate.
 2. The flexographic developer concentrate of claim 1,wherein the fatty acid composition consists essentially of oleic acid oran alkali metal salt thereof in an amount of at least 85 weight % and upto and including 90 weight %, based on the total weight of the fattyacid composition.
 3. The flexographic developer concentrate of claim 1,wherein the buffer compound is a carbonate.
 4. The flexographicdeveloper concentrate of claim 1, wherein the fatty acid composition ispresent in an amount equal to or less than 25 weight %, based on thetotal weight of the flexographic developer concentrate.
 5. Theflexographic developer concentrate of claim 1, comprisingethylenediamine tetracarboxylic acid or an alkali metal salt thereof inan amount of at least 1.5 weight % and up to and including 10 weight %,based on the total weight of the flexographic developer concentrate. 6.The flexographic developer concentrate of claim 1, wherein: a) the fattyacid composition consists essentially of oleic acid or an alkali metalsalt thereof in an amount of at least 90 weight % and up to andincluding 100 weight % of the fatty acid composition, and the fatty acidcomposition is present in an amount of equal to or less than 25 weight%; b) ethylenediamine tetracarboxylic acid or an alkali metal saltthereof is present as the one or more aminopolycarboxylic acids oralkali metal salts thereof in an amount of at least 1.5 weight % and upto and including 10 weight %; c) a carbonate is present as the buffercompound in an amount of at least 4 weight % and up to and including 8weight %; and d) water is present in an amount of at least 60 weight %and up to and including 80 weight %; all amounts being based on thetotal weight of the flexographic developer concentrate.
 7. A solidflexographic developer concentrate, consisting essentially of: a) afatty acid alkali metal salt composition consisting of one or moresaturated or unsaturated fatty acid alkali metal salts, each saturatedor unsaturated fatty acid alkali metal salt thereof independently having12 to 20 carbon atoms, the fatty acid alkali metal salts compositionbeing present in an amount of up to and including 60 weight %, whereinat least 85 weight % and up to and including 95 weight % of the fattyacid alkali metal salt composition is composed of one or more C₁₈ mono-or poly-unsaturated fatty acids or alkali metal salts thereof; b) one ormore aminopolycarboxylic acids or alkali metal salts thereof in anamount of up to and including 15 weight %; c) a buffer compound in anamount of up to and including 25 weight %, and optionally a glycol orpoly-glycol mono-ether co-solvent, enzyme, fluorescent whitening agent,perfume, biocide, fungicide, defoaming agent, colorant, bleach, bleachactivator, or surfactant, all amounts being based on the total weight ofthe solid flexographic developer concentrate.